1. Field of the Invention
Embodiments of the present invention generally relate to detecting 3:2 pull down in a video stream and using the detection to improve processing of the video stream.
2. Description of the Related Art
Telecine or 3:2 pull down is a process of converting motion picture film captured at 24 frames per second (fps) to interlaced video with a run rate of 30 fps (or 60 fields per second). This conversion is performed by distributing the frame content of the film into video fields such that every four frames of the film are “stretched” into five interlaced video frames (10 fields). The stretching is accomplished by duplicating two fields of the 24 fps content. FIG. 1 shows an example of 3:2 pull down applied to eight frames, A-H, of 24 fps content to generate 10 frames, 1-10, of 30 fps content. Each frame of the 24 fps content is divided into two fields, a top field and a bottom field.
The top and bottom fields of frame A become the top and bottom fields of frame 1, and the top and bottom fields of frame B become the top and bottom fields of frame 2. To create frame 3, the top field of frame B and the bottom field of frame C are used. To create frame 4, the top field for frame C and the bottom field of frame D are used. The top and bottom fields of frame D become the top and bottom fields of frame 5. This pattern is then replicated for the next four frames, E-H, of the 24 fps content to create frames 6-10 of the 30 fps content.
Telecined video may provide no overt information indicating that the video is telecined and/or the 3:2 pull down pattern may not be consistent throughout the video. For example, the pattern may be disrupted by editing of the video. Some detection techniques compare the differences between adjacent fields to look for the 3:2 pattern. However, such techniques may not be able to reliably distinguish between noise, slow movements, high frequencies, and interlaced content. Other detection techniques analysis the motion vector data from field to field. Such techniques may be quite complex and not suitable for use in resource limited embedded systems.